2. Field of the Invention
The present invention relates to vascular bypass grafts and, in particular, to a method of forming surgically implanted grafts which increase blood flow and reduce clotting and a method for making such grafts.
3. Related Art
Vascular disease is a leading cause of morbidity and mortality in the United States and throughout the world. The causes of vascular disease include diabetes, hypertension, renal failure, and smoking as well as many other etiologies. Vascular disease can affect any blood vessel in the body and commonly involves the coronary arteries, carotid arteries and the arteries of the lower extremities. The disease is caused by cholesterol, plaque, and calcium deposits which cause vascular wall thickening. Vascular wall thickening occludes the afflicted vessels by narrowing them, which reduces or in some cases, completely blocks blood flow.
Vascular disease leads to progressive narrowing of vessels secondary to plaque build-up within the vessel walls. This plaque is initially soft and initially not flow limiting. Eventually the plaque hardens and progressively becomes larger creating narrowing which becomes clinically significant limiting the body's ability to perform the necessary function of the organ or limb involved. For the heart it begins as chest pain on exertion and eventually a myocardial infarction. In the legs the progressive narrow leads to claudication (pain on exertion) and eventually leads to amputation and limb loss.
Vascular disease is currently treated in several different ways. Patients may engage lifestyle changes, changes to diet and exercise, and medical therapies such as cholesterol lowering drugs. However, for some patients, these non-invasive treatments are insufficient and surgical or invasive intervention such as bypass surgery or angioplasty are necessary.
Bypass grafts are used throughout the body to route blood around occluded or highly stenotic vessels secondary to vascular disease. Currently only single lumen, straight bypass grafts are available, whether created from man-made materials or harvested from a patient's body, cadavers or from animals. These straight bypass grafts are attached by a surgeon to a higher pressure, upstream blood vessel to a lower pressure, downstream blood vessel. They are most commonly used in the heart (coronary artery bypass) and in the extremities (peripheral bypass) with utilization in many other vessels less commonly adopted, such as use in the mesenteric arteries which supply the bowel. A bypass graft can connect or be provided in both short and long lengths, such as an axillary-femoral graft which is attached to the arm artery and passes along the lateral aspect of the chest and abdomen and is attached distally to the leg artery. They also can be used to connect from one side of the body to the other as in the Femoral—femoral bypass which attaches to one of the vessels in the groin then passes across the patient's pelvis and at its distal end attaches to the leg artery of the other leg.
All grafts, including grafts made from harvesting a patient's own vein from a donor site have the common problem of failure. Failure occurs when the grafts, through resistance to flow, has clinically significant decrease in blood flow or complete occlusion. The consequence of this is decreased blood flow to the body parts/areas that the bypass graft serves downstream from the graft. For example, a lower extremity bypass failure can lead to ischemia and possible tissue and even limb loss. The reasons for failure are secondary to grafts forming internal clot which ultimately leads to decrease or loss of flow. Blood clotting can occur for many reasons such as slow blood flow, vessel injury, intimal hyperplasia creating occlusion and history of prior clot formation and propagation, and as a result of a patient's increased propensity to form clot. Clotting can occur from one, or a combination of these factors.
A patient undergoing bypass surgery has a bypass graft, surgically implanted. The bypass graft provides a substitute route for blood flow to bypass an occluded region. The bypass graft is a tube structure with two ends. One end attaches on one end before the region of vascular occlusion, and on the other end to the patient's vascular system downstream of the occlusion. In this manner, the bypass graft improves the patient's blood flow around the occlusion.
The majority of bypass grafts function well over time, however, in a significant number of patients the bypass grafts themselves become occluded. Where a bypass graft becomes occluded, the patient must undergo another surgery or intervention to place a second graft or to open and reestablish flow to the original graft.
As a result, there is a need in the art for a bypass graft that can provide a route for blood flow while preventing occlusion which leads to graft failure. The description herein enables such a bypass graft as well as a method of implanting the bypass graft.